1. Field of the Invention
The present invention relates to protective garments. More particularly, the present invention relates to protective garments used in hazardous environments.
2. Description of the Prior Art
Protective clothing of many types are well known for many and varied uses including protection from fire, chemical liquids and vapors and other harmful substances Such clothing is often seen in suits for industrial workers, firemen, hazardous waste workers, chemical workers, race car drivers, airplane pilots and military personnel. Garments include not only complete hermetic suits, but also individual components such as trousers, jackets, gloves, boots, hats, head coverings, masks, etc.
Regulations restricting exposure to hazardous environments of various kinds, such as those contained in the Occupational Safety and Health Act, (OSHA) make it increasingly necessary to have better and more effective kinds of protective clothing. In particular, certain requirements by the U.S. Coast Guard and related requirements by other U.S. government agencies such as the Environmental Protection Agency (EPA) involve a total protective hermetic suit or unitary enclosures around the individual person to protect the worker from the widest possible range of hazardous materials.
Protective garments include woven and non-woven fabrics for disposable use. These garments are generally formed from various polymeric films or laminated plastic materials which are intrinsically resistant to dust or liquid penetration and in some cases impervious to chemical vapor penetration. The fabrics are generally spunbonded, meltspun or of non-woven thermoplastic material. The gas-tight suits must meet the permeation criterion of ASTM, test method D 739-85 and the liquid barrier suits must meet the penetration criterion of ASTM, test method F 903-84.
Encapsulated suits are required for "immediately dangerous to life and health" (IDLH) environments. These suits must be air tight and worn with a self-contained breathing apparatus (SCUBA). These are termed "HAZ MAT" suits and are designated as Level A suits under OSHA/EPA guidelines. These suits must be nonabsorbent, totally impermeable and resistant to a widest range of chemicals and reagents in liquid and/or gaseous forms. They should be fire resistant, meeting all the fabric requirements of the National Firefighters Protection Association, NFPA 1993. They should also be anti-static, meeting the fabric requirements of Anti-Static Charge Dissipation Test NFPA-99. Since these suits are worn by active individuals, they should be flexible, abrasion resistant, lightweight, and should maintain their impermeability while being used.
The garments presently available are almost invariably of thick construction and heavy in weight, and are often fabricated at least in part from materials impermeable to water or water vapor, such as natural and synthetic rubbers and elastomers, chlorinated rubbers, etc.
It is desirable to utilize an impermeable fabric which has a low melting point so as to have the ability to provide melt fusion bonding and which is chemically inert to a wide range of substances. The various fabric panels of the protective garment are usually overlapped and then sewn together. However, sewn seams cause needle holes which provide penetration sites by dust, liquids or vapors through the holes or the seams themselves and must be sealed by capping over them by adhesively bonding a suitable chemical resistant strip. Seams which are made with adhesives (hot melt or pressure sensitive) can peel apart upon flexing and kinking also can weaken the seam. The protective film or laminated plastic fabric seams must be fusion bonded sealed to form a barrier against solids (dust), gases and liquids while subjected to flexing and kinking in order to prevent toxic or harmful gases and liquids from permeating or penetrating the seams of the protective suit.
The optimum seam, which joins the various panels of laminated fabric or film to form a protective barrier against chemical vapors, should provide equal to or better impermeability than the laminated fabric against chemical vapors. Therefore, it is preferable to have a laminated fabric or film which melts to itself so that a tape of a plastic material having a melt index in the same range as the plastic barrier films can be used to fusion bond and form the seam. Fusion bonded in this manner, the seams of the laminated fabric or film provides excellent protection from contaminating dust, liquid and vapors.
When fabricating and bonding protective garments made from various plastic films and laminated plastic materials, the most difficult sealing problem is the bonding at stressed locations such as the zipper strip and the optically clear facepiece material to the plastic material which forms the protective barrier material for the garment.
A chemically resistant optically transparent facemask and a zipper for opening and closing the suit must be sealed to the protective plastic film in a gas tight seal. The gas-tight commercial zippers available are usually found on strips of polyvinyl chloride (PVC), polyethylene (PE), butyl rubber or neoprene rubber. The optically transparent facepiece material is generally made from PVC, TEFLON.RTM.FEP (fluorinated ethylene-propylene copolymer), TEFLON.RTM.PFA (perfluoroalkoxy resin) or polycarbonate. The surface of the protective film or laminated film to which the facepiece to be bonded is usually a polyolefin, a butyl rubber, neoprene, TEFLON.RTM., a polyester, an aluminized polyester, a polyurethane or a polyvinyl chloride.
The fluorocarbon polymers have excellent properties regarding heat, chemical resistance and optical clarity and are the preferred materials for the facepiece component. However, the poor surface energy of the fluorocarbon resin films results in poor adhesiveness. This property becomes a difficult problem particularly in adhering dissimilar materials used in the manufacture of protective garments. Obviously, the facepiece is a critical component of a protective garment suit. A suitable manner of attachment to the protective garment fabric has been a recurring problem both from the standpoint of manufacture and in providing the required rupture resistant and chemically impermeable seam at the attachment.
It is very difficult to form flexible gas tight seals or bonds between many dissimilar materials such as fluorocarbon and halocarbon polymers, rubbers, polyolefins, plasticized polyvinyl chloride, neoprene, butyl rubber, silicones, polyester, etc. An adhesive or bonding system is needed which can form strong, flexible, gas tight seals or bonds between chemically dissimilar materials particularly for a fluorinated ethylene-propylene copolymers and perfluoroalkoxy resins laminated to polyethylene, polyproplene, and/or PVC. The conventional adhesives used to bond such dissimilar materials particularly for a fluorinated ethylene/propylene copolymers and materials have the disadvantages of forming brittle bonds that crack on flexing or develop leaks due to differences in the coefficient of thermal expansion between the two sheets of material that are sealed together. Pressure sensitive adhesives such as atactic polypropylene, some low molecular weight thermoplastic polyesters and acrylates either do not form a strong bond to the dissimilar materials and begin to leak after flexing and/or kinking. Standard hot melt adhesives depend on mechanical locking of the fibers on the surface of the fabric and upon stress surface rupture (unitary film failure) occurs.
There is a difference between bonds that are heat sealed and bonds that are heat fused. A heat sealed bond involves the transformation of a solid material (hot melt adhesive) to a semi-liquid sticky state that flows and wets the surfaces, and which upon cooling, seals the dissimilar materials. Fusion bonding involves intermixing or alloying of molten resin under heat and pressure between at least two chemically dissimilar surfaces to be bonded. The flowing and intermixing causes at least the two dissimilar materials to yield a product with superior strength and sealing characteristics exhibiting total adhesive failure. Materials having the same chemical composition when subjected to heat fusion bonding will exhibit total cohesive failure.
The problems associated with the attachment of the facepiece involves the poor adhesion properties of the fluorocarbon per se along with the use of dissimilar materials as fabrics in the manufacture of protective garments.
U.S. Pat. No. 4,272,851 issued to Goldstein, which is herewith incorporated by reference, discloses a protective garment for use in hazardous environments. The body of the garment is formed of a non-woven spun bonded olefin having a polyethylene film laminated to one side (Tyvek.RTM.). The patent discloses a transparent front visor (not further identified as to the material used) sealed to an integral hood made of Tyvek.RTM., a seam-bondable material. It is not specifically disclosed how the sealing of the facepiece is effected although the other seams are ultrasonically welded. This procedure results in a seam which has inadequate resistance to rupture from shearing. In order to give greater strength against shear stresses, the patent further discloses adding a binding along the folded back seam, which binding is sewed on by traditional stitching means. While the multiple layers so stitched may be somewhat more protective of the body material, the facepiece does not undergo this step and remains subject to rupture. (See FIG. 6 of the patent). Further, the patent does not disclose the use of optically transparent halocarbon, particularly fluorocarbon plastics, more specifically, a fluorinated ethylene-propylene copolymer (FEP) or a perfluoroalkoxy resin (PFA) as a face visor. Polyvinyl chloride may be included to provide rigidity to the facepiece.
Therefore, there exists a need to fusion bond and seal chemically dissimilar materials so that the resulting bond is strong, flexible, impermeable to gases and liquids and when the bond fails from a sufficient of stress, the bond exhibits total cohesive failure. Such a bond and seal is necessary for affixing an optically transparent facepiece to a protective garment.